The present invention relates generally to pavement marking, and more particularly to the adjustment mechanism for a thermoplastic die box
Alkyd and hydrocarbon thermoplastics are commonly used to mark pavement surfaces with visible lines and symbols such as lane dividers and guide lines. In particular, thermoplastics provide a durable alternative to pavement painting, and are commonly used to mark street intersections, parking lots, and other high-traffic pavement surfaces from which paint would quickly wear away.
Thermoplastics are conventionally applied to pavement surfaces using a mobile applicator comprising a heated reservoir or kettle, and an application screed die. Melted thermoplastic is dispensed from the kettle at a controlled rate and applied in a thin layer atop pavement surfaces with the screed die. Some applicators further comprise secondary burners which heat secondary reservoirs or screed die. Many applicators burn pressurized gas, such as propane and butane, at secondary burners and to heat applicator kettles. Manually driven and self-powered applicators are both relatively common, and some applicators can be attached to and driven by vehicles.
Conventional thermoplastics must be brought to melt temperatures of 177 to 250° C. (350 to 480° F.) prior to application. Existing systems use a central mixer-melter to bring thermoplastics to these temperatures. Once melted, a load of thermoplastic from the central mixer-melter is transferred to the kettle of a mobile applicator for pavement marking. The applicator kettle is heated to prevent thermoplastic from resolidifying before it is applied to the pavement surface. Often, a single central mixer-melter may service a plurality of applicators on a job site.
In general, governmental regulations determine the thickness of the thermoplastic being applied to the road surface. In order to achieve this predetermined thickness, the thickness of the dispensed material must be changed. In addition, other environmental factors can change the application parameters (such as ambient temperature and surface roughness). In order to compensate for such variables, the screed die box needs to be variable. But the adjustments will need to take place in the field where there may be adverse conditions and/or limited mechanical facilities.